Bags made from thin films tend to zipper or otherwise tear when punctured or stressed. It has been long desired to reduce the tendency of such thin films to zipper and tear without significantly increasing the bag thickness or weight as required in ribbed bags shown in U.S. Pat. No. 3,193,604, for example. Attempts to accomplish such a desired result can be found in U.S. Pat. No. 3,265,789 or British Pat. No. 1,250,945 which impinge air on tubular film as it is being extruded. Some amount of thickness is provided by the cooling mechanisms of these patents but the mechanisms fail to provide a configuration of rib intensity, sharpness, strength and pattern necessary to maximize the tear strength of the film without significantly increasing the resin requirements and weight of the film produced. The present invention provides a process and apparatus for producing a film having extraordinary tear strength because of the characteristics imparted to the film by such process and apparatus.